In electronic devices, wiring circuit boards have been used and, as the wiring circuit boards, flexible printed circuit boards (sometimes referred to as “FPC”) have been widely utilized. In such FPC, adhesives are used (1) in the process of manufacturing FPC by adhering and laminating a conductive metal foil such as a copper foil or an aluminum foil to a heat-resistant base material such as a polyimide base material or a polyamide base material and (2) in the process of adhering FPC to a reinforcing plate such as an aluminum plate, a stainless steel plate, or a polyimide plate. As the adhesives for use in such adhesion of FPC, nitrile rubber (NBR)/epoxy resin-based adhesives and acrylic rubber/phenol resin-based adhesives (see, U.S. Pat. Nos. 3,822,175 and 3,900,662) have been widely utilized.
However, since the conventional acrylic rubber/phenol resin-based adhesives have non-pressure-sensitive adhesiveness at ordinary temperature (23° C.), temporary attaching operation cannot be performed at ordinary temperature at adhesion and pressure-sensitive adhesion of FPC in the manufacture of FPC and in the attachment of FPC to a reinforcing plate. Therefore, in a processing line, or the like, a special warming jig is necessary, and thus, a decrease in operating efficiency and danger to worker may accompany. Moreover, when it is intended to impart pressure-sensitive adhesiveness at ordinary temperature to the acrylic rubber/phenol resin-based adhesives, adhesiveness and heat resistance may be lowered and it is difficult to maintain a good balance between adhesiveness and heat resistance since elastic modulus is to be lowered for the impartment of pressure-sensitive adhesiveness.